The Soviet leadership once again has turned its attention to the chronic ailments of Soviet agriculture and, once again, it appears to be offering more of the same old medicine.

Despite the banner headlines and full-page speeches, the land reclamation program presented this week at a plenum of the Communist Party Central Committee is a continuation of policies in effect since 1965.

If there was anything new, it was a shift in emphasis away from the themes stressed during the era of the late Yuri Andropov, when the call was for better use of exisitng lands, and on inducing farm workers to improve their methods.

The approach taken by Soviet leader Konstantin Chernenko in his speech this week was in the tradition of bigger and bolder projects, harking back to the days of Nikita Khrushchev's virgin lands campaign. Where Andropov spoke in April 1983 of finding better ways of "turning over soil" on lands already in cultivation, Chernenko talks of "unfolding land improvement on a large scale. The matter at issue is not the shifting of accents in our directives but a search for truly innovative and creative approaches," Chernenko said.

Yet the goals laid out by Chernenko and Soviet Premier Nikolai Tikhonov on Tuesday for new lands to be claimed for agriculture through drainage and irrigation by the year 2000 -- representing a 50 percent increase to between 121 million and 130 million acres -- were hardly new. On Oct. 3, the same numbers -- down to the last irrigated acre -- were matter-of-factly spelled out in a routine update issued by Nikolai Vasiliyev, minister of land reclamation and water management.

The most intriguing revelation of this week's plenum was not mentioned by Chernenko but was buried in the full text of Tikhonov's exhaustive report on land reclamation printed in the official party daily Pravda on Wednesday. There, Tikhonov indicated that a controversial plan to divert water from two gigantic Siberian rivers is moving ahead.

The Siberian river plan would redirect the flow of the Ob and Irtysh rivers away from the Arctic Ocean toward the parched lands of Central Asia, through a mammoth canal about 1,530 miles long.

Both Soviet and western experts are concerned that such tampering could have a critical effect on weather patterns by reducing the amount of ice in the Arctic.

Tikhonov's cautious mention of the project indicates that its scope still has not been determined. "In the near future, we are going to complete design work on the transfer of part of the flow of Siberian rivers in the regions of the Urals and west Siberia, Central Asia and Kazakhstan," he said, adding that linking of the system will be considered later.

At the least, his remarks mean that the plan is not dead, and while Chernenko cautioned against hasty decisions that harm nature, he made a point of saying that the "country's south" -- Central Asia -- will be a prime beneficiary of future irrigation.

While placing great store in land reclamation, Chernenko also indicated dissatisfaction with the productivity of land reclaimed in the past 18 years.

He chided managers for wasting water, called on ministers "to stamp out dissipation of effort" and said it was "unforgivable" that only one-third of the nation's 81 million acres of reclaimed lands so far had met production quotas.

These points were made last March by Mikhail Gorbachev, since 1979 the Politburo member in charge of agriculture. The difference was that Gorbachev then seemed to indicate, as had Andropov, that the best way out of the Soviet Union's agricultural impasse was to correct these problems, rather than embark on more land reclamation projects.

"Reclaimed land is not used efficiently enough," Gorbachev said. "Over the recent years, funds have been channeled into new land reclamation systems at the expense of modernization and maintenance programs."

Gorbachev's speech last March also emphasized the need to support the nation's private holdings, which, although they include only 1.4 percent of Soviet farmlands, produce more than 30 percent of the nation's meat, milk and eggs, and more than 50 percent of its vegetables and berries.

Putting the Soviet farm problem in more human terms, Gorbachev spoke of the importance of making the farm worker aware of the goals set for him, and of letting him see "the direct relationship between his work and his pay."

This also had been Andropov's approach -- a trend to toward greater local control, and greater attention to working conditions on the land.

While Chernenko made passing endorsements of some reforms stressed by Gorbachev, the overall theme was on claiming new land for farming.

The fact that Gorbachev did not speak at the plenum is taken as a sign that he is no longer responsible for agriculture, perhaps because, as the second-ranking member of the party, he has moved on to other tasks.

An interesting aspect of the plenum this week was that it was called at all. Its timing was unusual in that it will not be followed by a regular session of the Supreme Soviet, and, given that its subject matter could not have come as a surprise to the 312 members of the Central Committee, who gathered from the far corners of the nation, its purpose was unclear.

In terms of agricultural policy, it simply may have been keyed to the growing realization that this year will bring another bad grain harvest. Press reports here already have advised of the drought that set back yields in regions east of the Volga River, notably the grain belt in Kazakhstan.

This year, U.S. Department of Agriculture analysts are estimating the Soviet grain crop at 170 million tons, the lowest since 1981 and the sixth in a row to fall far below the official goal.

The bad grain crop and continuing reports of mismanagement and waste from the countryside only reaffirm the late Leonid Brezhnev's remarks in November 1981 that food production is "economically and politically" the nation's central problem.

In 1981, there were critical shortages of certain foods in the Soviet Union, notably meat. The next year, Brezhnev launched his food program, emphasizing imports, encouraging private plots and other reforms. Meat production is up 6 percent through the first nine months of this year, and "substantial" increases in vegetable and fruit production were reported.

But as Chernenko noted, "The problem of providing the population of many cities with foodstuffs -- above all meat -- is still acute."